Wednesday, 8 January 2020

variational principle - Why vary the action with respect to the inverse metric?


Whenever I have read texts which employ actions that contain metric tensors, such as the Nambu-Goto, Polyakov or Einstein-Hilbert action, the equations of motion are derived by varying with respect to the inverse of the metric, i.e. indices are in superscript.



Why is this? Why not vary with respect to simply the metric tensor? Or is it just a convention/preference?




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